I’ve recently started to get this horrible clunk on my gsx750.

It happens mostly seemingly when I’ve slowed down for a junction or something and then I’m accelerating up again.

Seems to disappear at higher revs where the engine runs smoothly, but building up to speed I can hear a clunk and even feel it a bit through the pegs.

I’ve checked everything I can think of and can check easily.

Chain tension, chain movement (removed it and checked all the links move ok), checked sprocket bolt is tight, rear sprocket is tight, chain sliders on swingarm are all running good, sprockets don’t seem worn.

Anyone got any ideas what to check next?

Here’s a short clip of it up on my paddock stand running in fourth.

You can hear that occasional clunk and the chain looks to be jumping about a lot, though obviously it may run differently sat on it and suspension compressed.

Have you got a hugger fitted? Maybe touching the wheel?

No hugger no..checked everywhere for any fouling..all good

That’s normal when running on the paddock stand, there’s no load on the rear wheel so the inertia of the wheel causes the chain to flap. It won’t happen on the road as there’s load going through the wheel and load on the suspension. Also, how often will you be in 4th gear at idle?

Now, the ‘clunk’ at low revs – how low revs are we talking?  Could just be the engine being lumpy down low and causing the chain to slap when at low revs. If you can feel it through the pegs, I’m gonna say you’re in to high a gear and labouring the engine. These things red line at 10k+ rpm, they’re not meant to be ridden at 1500.

As yours is an IL4 it should only happen at just above idle, get to 2k rpm and it should smooth out. A v-twin on the other hand will be lumby under 3-4k.

Yeah I expected a little on the stand but it does happen on the road.

It’s lower revs and really, when I back off on the revs. I can sometimes feel it through the pegs even though I might be going say 50mph.

It’s always been really smooth. This is a new thing last few rides.

How old is the chain? Is it a lot slacker at some points when you turn the wheel slowly. If it’s time for a new chain might be worth changing the sprockets as well.

My only experience of that was on a training center Honda 500, it was almost unrideably shagged. Close the throttle and there was enough of a jolt to throw you forward like the back wheel locked up.

If the chain and sprockets absolutely, definitely,aren’t worn then have you checked for play in the gearbox outpush shaft? Or does it have a cush drive?

How low revs are we talking?

When you say ‘back off on the revs’ do you mean pull in the clutch so the bike is idling whilst doing 50mph?

Have you drained the gearbox oil recently? Anything in the oil?

Take the clutch cover off, take the spark plugs out – turn the clutch basket by hand – any notching/clunking? Try it in every gear.

Cush drive rubbers?

Cush drive rubbers?

No, it’s just the way I walk 😉

Cheers. Some things to try there. I’d say it’s in about 1-6k revs or thereabouts. Really weird.

I was convinced there was a loose rotor bolt or something physical catching on something else but I just can’t see anything. Checked everything is tight.

The chain isn’t that old. I mean it’s not a super expensive one but it seems to pivot fine off the bike. The sprockets look pretty good, with no hooking to them or anything.

I’ll keep trying. Was hoping to find something more obvious before the pita of draining the oil and removing covers and that..

I haven’t had a motorbike for 35 years but when I had an issue like that it was the cush drive rubbers.

check the chain for wear too, try and lift it off the rear sprocket, it shouldn’t have much play.

Another for Cush drive rubbers

Cheers.  I’ll check my cush drive too, although it’s doing an occasional big clunk up on the stand there too and not under load so not sure it’ll be cush drive.

Sounds like you’ve lost a chain roller.

Stick the bike on the stand and rotate the wheel look at each link in turn. If one of the rollers is missing you’ll just have a skinny pin. That doesn’t engage with the teeth, rides on top and clunks in place.

You wouldn’t think it would be possible to lose a roller, but I’ve seen it twice.

Is the throttle cable adjusted so it’s nice and tight? If there’s any slack there is can amplify the feel of any drivetrain slop.

As been mentioned,check that the gearbox sprocket it tight on the splines.My wifes Hornet developed a similar problem and it was slightly worn splines that accelerated wear on the sprocket.A genuine honda sprocket along with some stud lock helped mask the issue.

cush drive rubbers is a big ‘clunk’ when the clutch is dropped and similar big clunk when rolling off or on throttle.

The frequency isn’t correct for chain issues – that would be a constant rythmic ‘chink…chink…chink…chink…chink’ type frequency.

Your issue looks very high frequency/low load so something like a gearbox bearing having shat it’s cage.

Do a bit of roll on roll off throttle action to figure if it’s secondary drive related ie output shaft sprocket.

Do a bit of roll on roll off throttle action to figure if it’s secondary drive related ie output shaft sprocket.

Very difficult to tell. Do you mean on the stand? I’ve been doing little accelerates and looking down or touching parts of the casings, but that’s not ideal for obvious reasons. Hmmm, I wonder if it would fit on my rollers…😃

I wanted to run it with the clutch cover removed so as I might see the sprocket jump or anything, but you can’t start it without the clutch in and the cover operates the push rod.

I wonder if I ran it without the chain I might isolate that from the scenario? 🤔

Put it in gear and try to rotate the rear wheel back and forth? That would show up any play.

Nothings ever simple is it? Presumably the clutch cut out is a switch at the lever – could you remove the connectors and short it with a bit of wire?

Wouldnt be a stiff link then?

I wouldnt bother trying to run it with an exposed clutch – I was meaning to turn the engine over by hand using the clutch basket with the plugs removed to see if you can feel any notchyness.

Roll on/off throttle to try determine is it a single loud deep clunking/thumping from the rear that’s in time with the bike (cush rubbers), or does it multiple smaller chink chinks from the middle of the bike (possible worn output shaft sprocket).

Or as above get someone to bang the rear wheel back and forth with the bike on a stand.

Don’t run the engine on a stand whilst investigating faults – your fingers will thank you.

Wouldnt be a stiff link then?

Nah, checked it all off the bike. They all resist a little on account of the rubber O-rings but they’re all pivoting ok.

I wouldnt bother trying to run it with an exposed clutch

I just meant an exposed front sprocket actually, not the clutch itself.

Presumably the clutch cut out is a switch at the lever – could you remove the connectors and short it with a bit of wire?

Yeah good shout. Might try that. Silly modern bikes. I’m used to older bikes (although this one is year 2k). I demoed a triumph a couple of years back and had no idea about the whole clutch in when starting thing. Had to phone the dealer after stopping for a photo opp and couldn’t start it 😬

I demoed a triumph a couple of years back and had no idea about the whole clutch in when starting thing. Had to phone the dealer after stopping for a photo opp and couldn’t start it 😬

You’d not be the first! My neighbour spent a whole weekend chasing faults on a bike he’d inherited, until I told him (as a Triumph owner myself) that info. He wasn’t amused.

Been running it up on the Jack with the sprocket cover removed. Still clunks and jumps about like a mofo.

I drove into a bike shop and they had a quick go up the road and basically couldn’t think what it might be either. I suggested I changed the chain to rule that out, but the dude was pretty sure that the chain and sprockets looked fine and well adjusted.

Here’s a vid of it running without the sprocket cover.

You can see it clunk and skip a bit, but the sprocket itself seems dead consistent and true.

Like I say, it only happens when accelerating. As soon as I pull the clutch or shut the throttle the noise goes.

I’ve got it booked into the bike shop on Monday for them to take the clutch out and have a bit of a deeper delve.

😐

How many miles has it done? The rubbers on the back of the clutch basket might be fubar? If it’s a two piece clutch cover you can take the outer off and try rocking the basket back and fore. May even be a broken clutch plate which might explain it going away when you pull the lever in.

It’s only done 20k or so. Pretty low.

The bike shop are going to pull the clutch off Monday so hopefully they’ll see what’s what.

A bloke on a motorcycle forum where I’ve also put this, reckons I Defo need new chain and sprockets. I mean, they’re jumping a bit I guess but I’m not too sure how much is normal given the lack of weight on the back wheel.

It is possibly that, I’ve had chain tension alone doing some horrible things to drive train smoothness. Wouldn’t have thought that pulling the clutch would have made a difference if it was that though, not impossible I suppose.
Do let us know what they find, I’m intrigued.
Engine mounting bolts are all tight?

Yeah, I’ve done a bolt-around, checking everything.

Gearbox especially if it goes away with the clutch in/isolates drive and the frequency of jumping is the same frequency as the drive sprocket rotating if you know what I mean?
Have you drained the oil yet?

Is this perhaps the motorised version of chain suck? Chain and sprockets are a bit worn, chain gets replaced, now the new chain doesn’t fit the worn sprocket and you’re stood there going “well, the chain’s not that old”?

Either that or drop the rear wheel back a quarter of an inch. (-:

Not drained the oil yet. Could do that today I guess as I can’t ride bicycles for a wrist pain at the moment.

The chain is the correct tension. It’s unloaded at the moment so when the bike is on the floor you get a bit of growth, very much like a suspensionated bicycle.

Have you drained the oil yet?

Going to leave that as I guess the bike shop will be doing that to remove the clutch assembly.

Just to update anyone interested, just got the bike back from the bike shop.

They removed the clutch basket and inspected everything. Clutch plates all good but they did find that there was slack in the engagement/pick up of the clutch and play in the basket or main shaft.

So, it’s not been fully diagnosed as such but it’s looking likely that it’s something going on internally.

Not sure what to do really..obviously I don’t want to do any damage, but with it being summer, I also don’t want to or have the time to strip it right down to the gearbox when I’d rather be riding.

The bloke said it’s likely a days labour for them plus any parts needed to strip and rebuild it, so I’m more that likely looking at about 6-800 quid I guess.

Not sure what to do really. Bike cost me £1300 and I love the bike, and have already done some custom stuff on it which is what I’m aiming to do more of, but obviously that’s a lot of money on a year 2k bike.

Don’t like modern or faired bikes though. So hmmm.

Cheers for any help given in this thread. Much appreciated. I guess the story isn’t done just yet.

https://revtothelimit.co.uk/index.php

HAve an ask over on mine too mate, some of them may have seen similar.

I would have thought new chain and sprox would sort that out especially if it’s the original, would of thought the clutch was an issue, that would cause either dragging or slipping, if the plates are OK and the basket isn’t notched I wouldn’t worry about that side of things.

If it’s not the C&S it could be the splines on the output shaft (were the front sprocket’s attached) that’s worn – caused by the chain being to tight ?

Plenty of clutch baskets for under £50 on eBay – some complete assemblies. Get yersen a Haynes manual and stick one on together with a new C&S.

Yeah but the shop mechanic has had the clutch all out. Says the bearing is fine, the clutch is all fine, and the chain and sprockets are all fine and well adjusted.

I think he meant there is a slight rotational delay in pick up to the final drive, and that there was slight lateral play in the clutch basket. The clutch itself is fine, but I guess the shaft it’s running on has a little play.

I don’t know. I mean they didn’t really overwhelm me with details of what they found, but suggested they think it’s an internal issue and so anything else they do would be part of a gearbox rebuild. 💰